The formation of a lubricating film on metals prior to their cold working typically consists of the following two separate steps in the case of light cold working operations: the initial formation of a conversion film on the surface of the workpiece as a base layer treatment; the subsequent formation on this film of a lubricating film through the application of a lubricant. Thus, the complete lubrication treatment process comprises both a conversion step and a lubrication step.
Very high pressures (surface pressures) generally occur between the workpiece and tool during the cold working of metal. As a result, when the crystal lattice spacing (lattice constants) of the tool and workpiece are similar, the workpiece and tool ultimately weld together and bond to each other. These regions of the tool and workpiece are then torn away, leading to the occurrence of the phenomenon known as seizure. Direct contact between the workpiece and tool must therefore be avoided in order to prevent this problem. This objective is accomplished mainly through the use of a base layer film formed by conversion treatment as described above. At present, lubrication treatments consisting of the combination of such a base layer film and an appropriate lubricant are in widespread use in the metal cold working sector. The quality of the lubrication capacity exercised by the films formed by such lubrication treatment processes is related to the performance of the top layer lubrication film, but it is primarily controlled by the performance of the base layer conversion coated film.
On the other hand, recent remarkable advances in metal working technology have made possible operations even under mechanically extremely severe working conditions. However, the lubrication performance has not kept pace with these advances, and at present the performance limits of the base layer film define the limits of the lubrication performance. It is for this reason that major improvements in the performance of the base layer film (the so called lubrication film carrier) are desired.
Conversion treatment baths based on inorganic acid or low molecular weight organic acid (oxalic acid, etc.) are a technology already known as a useful point of departure for improving the lubrication carrier performance of the base layer films. Japanese Patent Application Laid Open [Kokai or Unexamined] Number Sho 62-174386 [174,386/1987] is an example of the addition of organic polymer to such conversion treatment baths in order to bring about an improvement in lubrication performance. Here, an improvement in lubrication performance is obtained by improving the film's adherence through the addition of water soluble organic polymer (excluding proteins) to an oxalate based film forming agent. The water soluble organic polymers listed for addition in the referenced patent are nonionic and have highly hydrophilic structures. In tests run by the present inventors, moderate improvements in the lubrication performance were observed, but major performance improvements were not achieved. Examining this matter from the perspective of the essential nature of lubrication, films that contain these highly hydrophilic structures do bring about a reduction in contact between tool and workpiece basis metal, but they lack the high level lubricating property of simply reducing the friction coefficient that operates between the film and tool surface.